A power breaker has been disclosed, for example, by EP 0 006 637. It is known from this publication that the force produced in a current loop can be used both for increasing and for decreasing the force between the contact members. Both functions are very useful for power breakers and are used in many different ways. An increase in the force between the contact members is desirable if the time at which the switching contact arrangement opens is intended to be entirely dependent on a protection device, for example an electronic overcurrent release. A prerequisite for this so-called selective response is that the contact members remain closed until the current is at its peak, since otherwise premature erosion of the contact members and other severe damage may occur. A current loop allows high-current-density forces, which are produced in particular between the interacting contact members and are equal in value to the square of the current, to be compensated.
In contrast to this, current-limiting power breakers have the characteristic that the contact members are opened directly in the event of a high current even before a protection device responds. This can be achieved or assisted by a current loop of the type mentioned. In combination with the action of an arc-quenching chamber, the electrical resistance of the switching arc formed when the contact members are separated in this case limits the current to a value which is acceptable to the power breaker and the associated switchgear.
The fact that a considerably different construction is required for the switching contact arrangements for increasing or decreasing the contact force adversely affects the cost-effective production of power breakers. Consequently, selective and current-limiting power breakers known to date differ in major structured features.